This invention relates to a windshield wiper arm assembly, particularly adapted for use on an operator's cab of a construction vehicle. The cab normally comprises a slidable lower windshield equipped with a wiper arm assembly for wiping the windshield in the event of rain or the like. Should the operator desire to raise and thus open the windshield for ventilation purposes, the wiper arm assembly, including its blade, will tend to move into the path of the windshield. In addition to deterring reclosing of the windshield, the wiper arm assembly will be subjected to damage. The wiper arm assembly may also be subjected to damage upon inadvertent actuation of the wiper arm assembly when the window is open.